The electrical conduction system of the heart creates specific electrical signals, electrical energy distributions and behaviors thereof which are indicative of specific locations in the thoracic cavity and/or of specific heart functions or conditions. When measured endovascularly, i.e., from within blood vessels or from within the heart, certain parameters of the electrical activity of the heart can be used to identify specific locations in the cardiovascular system and/or functional conditions, normal or abnormal. Moreover, by locally and accurately identifying the location and the type of condition, therapy of such conditions can be optimized and the effect of the therapy monitored in real-time.
Two types of clinical applications are typically addressed. The first is related to guiding endovascular devices through the cardiovascular system, while the second is related to the non-invasive or the minimally invasive remote monitoring of the electrical activity of the heart.
The guidance, positioning, and placement confirmation of endovascular catheters are necessary in a number of clinical applications, such as, for example:
1. Central venous access, e.g., CVC, PICC, implantable ports;
2. Hemodialysis catheters;
3. Placement of pacemaker leads;
4. Hemodynamics monitoring catheters, e.g., Swan-Ganz and central pressure monitoring catheters; and
5. Guiding guidewires and catheters into the left heart.
The location of the catheter tip is very important to the patient safety, the duration and the success of the procedure. Today's golden standard for confirming the target location of the catheter tip is the chest X-ray. In addition, there are currently two types of real-time guiding products available on the market, which try to overcome the limitations of chest X-ray confirmation: electromagnetic and ECG-based. In hospitals where real-time guidance is used results have improved in terms of reducing the number of X-rays, the procedure time, and the cost of the procedure. Under real-time guidance first-time success rate has typically increased from 75%-80% to 90%-95%. In addition, in hospitals where ECG guidance is used, e.g., in Italy, Belgium, Germany, chest X-ray confirmation has been eliminated for more than 90% of the patients. Electromagnetic systems are used mostly in the United States while ECG-based systems are used mostly in Europe. Amongst other factors which determine the difference between the markets in the United States and Europe in terms of technology adoption: a) type of health care personnel allowed to perform procedures: nurses have more flexibility in the United States, b) type of devices placed: PICCs are placed more and more often in the United States, c) price sensitivity: the European market seems to be more price sensitive, and d) the current guiding devices are commercialized by specific manufacturers to work exclusively with their catheters: market penetration of the guiding systems reflects the market penetration of the catheter manufacturer.
It was also found that different opinions exist regarding where the target tip location should be: for example, lower third of the SVC or RA. Therefore guiding technologies should allow for discrimination of these locations. The chest X-ray, which is the current golden standard does not always allow for such discrimination requiring an accuracy of typically better than 2 cm. Also, because ECG-based systems make use of physiological information related to the heart activity, their ability to guide placement is accurate with respect to the anatomy. This is not the case with electromagnetic guiding systems which measure the distance between the catheter tip in the vasculature and an external reference placed typically on the patient's chest. Because of this aspect, ECG-based systems can be used to document the final result of the catheter placement potentially replacing the chest X-ray as the golden standard.
One of the most valuable diagnostic tools available, the ECG records the heart's electrical activity as waveforms. By interpreting these waveforms, one can identify rhythm disturbances, conduction abnormalities, and electrolyte imbalance. An ECG aids in diagnosing and monitoring such conditions as acute coronary syndromes and pericarditis. The heart's electrical activity produces currents that radiate through the surrounding tissue to the skin. When electrodes are attached to the skin, they sense these electrical currents and transmit them the electrocardiograph. Because the electrical currents from the heart radiate to the skin in many directions, electrodes are placed at different locations on the skin to obtain a total picture of the heart's electrical activity. The electrodes are then connected to an electrocardiograph device, or computer, and record information from different perspectives, which are called leads and planes. A lead provides a view of the heart's electrical activity between two points or poles. A plane is a cross section of the heart which provides a different view of the heart's electrical activity. Currently, the interpretation of an ECG waveform is based on identifying waveform component amplitudes, analyzing and then comparing the amplitudes with certain standards. Modifications of these amplitude components are indicative of certain conditions, e.g., the elevation of the ST segment or of certain locations in the heart, e.g., the amplitude of the P-wave. In today's practice ECG monitors are widely used to record ECG waveforms. More and more often applications are made available for automatic identification of the ECG amplitude components. In certain cases tools are available for decision making support and for automatic interpretation of ECG amplitude components with respect to underlying heart conditions.
Remote patient monitoring is a well established medical field. Still remote monitoring of heart conditions is not as widely accepted as it would be need and possible. One of the reasons is related to the relatively complicated way of acquiring signals related to the heart activity, in particular ECG signals. Another important limiting factor of the current remote monitoring technologies is the use of communications channels, like the telephone line, which are difficult to interface with at both the patient and the physician ends.